Recreational vehicles, motor homes, trucks, boats and the like, particularly those of the larger variety, often have a plurality of water and coolant circuits. A first circuit may extend from the engine of the vehicle or boat and is typically used for heating the interior or the vehicle or boat. A second circuit may extend from an auxiliary heater which may also be used for heating when the engine is not operating. A third circuit may extend from a source of potable water used for cooking and other personal use. To assist in the significant movement of coolant and potable water, it may be required to use two or more heaters or additional pumps to supply the necessary thermal energy for the heating and also for fluid movement. Of assistance to the flexibility of the system is the distribution module disclosed in our United States patent application serial no. 20050284948 entitled DISTRIBUTION MODULE FOR WATER HEATER filed Dec. 29, 2005, the contents of which are incorporated herein by reference.
For smaller motor coaches and smaller boats, the use of a distribution module and externally located pumps may be unnecessary. In such event, it would be useful to have the burner, the various pumps, the heat exchanger, the expansion tank and the overflow bottle in a single location within a single heater casing. The casing would conveniently be relatively small to take advantage of the reduced space available on a smaller motor coach or a smaller boat.
Heretofore, the exhaust manifold connected to the burner tube has been designed for operation atop the coolant tank. The heater, being used for both RV and for marine use, conveniently requires an exhaust manifold which will allow an exhaust duct to exit the exhaust manifold in an “up” configuration for marine installations and a “down” configuration for RV installations. The exhaust manifold, therefore, was designed to extend beyond the end of the burner tube within the coolant tank so that the exhaust manifold could have either an up or down type exhaust configuration without modifying the coolant tank. This required more space within the coolant tank which was unnecessary and undesirable.
A further disadvantage with existing systems is that the burner tube is generally located in the center of the coolant tank or at least on the vertical plane defining the center of the coolant tank. The heater heats the coolant fluid unevenly because of the conflicting directions of flow of the heated coolant and there may be zones of coolant at different temperatures within the coolant tank. This affects efficient operation of the heater where precise coolant temperatures and predictable fluid flow are desirable.
Yet a further disadvantage of existing systems is the use of a pump which is connected directly to the expansion tank which receives coolant from or provides coolant to the coolant tank. A level switch is typically positioned within the coolant tank and when the coolant is low, the level switch terminates operation of the heater. By this time, however, the expansion tank may be empty and the pump thereafter runs dry before terminating operation. Air is introduced into the fluid lines which is not desirable and is inconvenient.
Combustion burners are used in heaters incorporated in boats, recreational vehicles, trailers and the like as is well known. Some of such heaters use diesel fuel and others use propane or liquefied natural gas. In some applications, such heaters are used to supply heated potable water as well as to supply a heated coolant used for space heating within the vehicle or vessel. The heated potable water is generally heated using a coolant which circulates through a heated coolant tank and exchanges heat with the water by way of a heat exchanger. Such a system is described and illustrated, for example, in our U.S. Pat. No. 7,036,746, the contents of which are incorporated herein by reference.
Heretofore, the heat exchanger has been located externally of the casing at a location remote from the heater. Such an configuration has a remotely located heat exchanger with a circulation pump to circulate the heated coolant is known. The use of such a configuration is useful where the space sought to be heated is large and where the temperature of the coolant circulated to the radiators is kept at a higher temperature for a longer time period. This is generally the case in larger motorhomes or recreational vehicles and larger marine vessels. The problem with such remotely located heat exchangers and water pumps is that the price increases because of the additional components necessary to utilise such a distribution module.
In some applications, however, where the space sought to be heated is smaller and where price is an important consideration, it is desirable to incorporate the heat exchanger within the heater casing. In that case, the number of components used can be reduced and the hoses used for circulating the water to the radiators and to the potable water circuit can be kept to a minimum length. Various improvements have been discovered in this configuration which enhances the combination heater and heat exchanger.